The myocardial innervation, its ontogeny, and its role in the function of cardiac tissue has been the subject of intensive investigations. Recent observations suggest that, in the adult, imbalances in the autonomic innervation to the heart may play an important role in the genesis of cardiac arrhythmias. A major obstacle in investigations of both the ontogenesis and pathophysiology of myocardial innervation has been the lack of a suitable preparation in which such studies can be carried out. The research proposed in this grant will utilize a unique cardiac preparation, fetal rat hearts transplanted to the anterior chamber of the eye. Such grafts develop functional autonomic innervation from the nora renergic and cholinergic nerve fibers of the autonomic ground plexus of the iris. The heart transplants are easily studied electrophysiologically as well as histologically, providing the basis for correlative studies of the morphological and physiological development of myocardial innervation. In addition, the preparation is well suited for intracellular recording atrial, ventricular and atrio-ventricular tissue, permitting a detailed electrophysiological analysis of cardiac arrhythmias and the role of autonomic inputs.